"This is huge," said Marco Caceres, senior analyst and director of space studies at Teal Group. "It would break up a monopoly and has the potential to save the taxpayer an awful lot of money."

This is not the first time the Russian-made AJ26 engines have caused problems, Marco Caceres, an analyst at Teal Group Corp., wrote in an Oct. 31 note. In 2007, the Sea Launch Zenit 3SL exploded because of an engine clogging and SpaceX failed to launch its Falcon 1 in March 2006 due to engine failure, he wrote.

If the engine proves to have been at fault in the latest explosion, it would be easier for Orbital to replace them rather than to attempt a repair, Caceres said in a phone interview today. "Their confidence in the engine was never high," he said.

Orbital's stock dropped 15 percent after the accident, and the company will likely have to postpone its resupply launches while it figures out what went wrong. If the problem can't be quickly fixed, according to Marco Caceres, director of space studies at the defense consultancy the Teal Group, Orbital may have to delay for several years while it works on a replacement, at which point it would risk losing its NASA contract.

NASA is "looking for cheaper access to space," said Marco A. Caceres, a space analyst at the Teal Group, a consulting firm in Virginia. The trouble, he said, is that reliability and price are often tied together.

"It may be unreasonable to expect to pay under a certain amount to get a reliable vehicle," Mr. Caceres said. "That comes at a cost."

Marco Caceres, director of space studies at the Teal Group, a consulting firm, said that "in an age where it is very expensive to fly these vehicles, the pressure is to do the minimal amount of test flying."

"So that may be something we have to take a look at," he continued. "Everyone seems to be in need of more money to conduct more flights, so the pressure is to start operational flight too soon. Maybe we are being unreasonable here."